This invention relates to methods and apparatuses for imaging arterial structures and more particularly for ultrasonically imaging epicardial arterial structures.
A conventional way of obtaining ultrasonic images indicating the condition of blood vessels, particularly arteries in the vicinity of the heart, involves insertion of an ultrasound imaging catheter directly into the artery of interest. This type of catheter, referred to as an intraarterial catheter, typically is inserted into the femoral artery and is then guided, such as with the aid of fluoroscopy, to the artery to be imaged. When in place, the catheter is activated to generate a scanning ultrasound signal which is reflected from the inner wall of the surrounding artery. The reflection signal is received by a suitable transducer and an image indicative of the cross-section of the artery is developed with the aid of electronic circuitry.
There are a number of drawbacks to this method. Since the catheter must pass through the artery, it can only image arterial sections whose interior diameters are sufficient to enable the catheter to pass through. Often arterial diseases produce blockages which can narrow an artery to the extent that the area with the blockage is too narrow for the catheter to enter. Thus the section of an artery of most interest to a physician frequently cannot be imaged with an intraarterial catheter.
Another disadvantage associated with the use of intraarterial catheters is that they can cause serious complications in patients. The introduction of a catheter into the relatively high-pressure arterial system presents a serious risk of arterial injuries such as arterial perforation, arterial thrombosis, myocardial ischemia and infarction. Due to these dangers, physicians are often reluctant to utilize intraarterial ultrasound imaging. This further impairs the usefulness of the technique.
It is the object of this invention to provide methods and apparatuses for developing images of arteries which do not suffer from the aforementioned disadvantages of the prior art.